This invention relates to hot melt adhesives comprising a blend of an isotactic thermoplastic polybutylene copolymer or a low density ethylene polymer with a solid benzoate plasticizer and a tackifier. Adhesives having this composition have been found to possess a unique combination of good open time and a delayed but increased crystalline character making them especially suitable as temporary adhesives for operations such as palletizing or those requiring a non-destructive bond.
Hot melt adhesives are bonding agents which achieve a solid state and resultant strength by cooling, as contrasted with other adhesives which set or harden by chemical reaction or loss of solvent or water vehicle. Prior to heating, the hot melt adhesive is a thermoplastic material in the form of a 100% by weight solid. Application of heat melts the adhesive so that it can be readily applied to the substrate desired. After removal of heat, the adhesive returns to the solid state by simple cooling.
Hot melt adhesives are widely used in industry for various applications including packaging, bookbinding, personal care products such as disposable diapers and sanitary napkins, and labeling. In order to satisfy the different property requirements in these and other applications, adhesive compositions are based on combinations of polymers and copolymers such as polyethylene, other polyolefins or mixtures, ethylene-vinyl acetate copolymers, polyamides, polyesters and block copolymers rubbers. Additives may also be included to modify and improve properties such as melt viscosity, peel strength, flexibility and stability and typical ones include waxes, oils, terpene resins, rosin derivatives, phenolic resins and coumarone-indene resins.
The isotactic polybutylene copolymers are known to be useful in hot melt adhesives because of desirable property attributes including long open time and their slow crystallization rate as noted in U.S. Pat. Nos. 4,568,713 and 4,956,207. However, such polybutylene copolymers and known adhesive compositions containing these copolymers do not possess the properties desired for a temporary adhesive of suitably long open time and very crystalline nature. These properties would provide a non-destructive, cohesively weak or break away bond that is needed in certainindustrial that is needed in certain industrial applications such as palletizing where articles, including cases and cartons, are placed on base pallets for temporary storage or transport.